Tunnel not working after reboot for some time

[disch]

Hello,

after a reboot of the client machine that carries the tunnel client (Windows XP) the tunnel isn't working for some time (sometimes hours or much longer).  After this timeframe the tunnel starts working, i.e. I can ping the tunnel server and IPv6 traffic thru the tunnel is working.  It's the same with the tunnel if the DSL connection was lost and restored again.  The client is NAT'ed behind a router.

Why this long time until the tunnel starts working?

Removing and adding the tunnel doesn't help.

Regards

Uwe